As the demand for optical devices, such as liquid-crystal display devices, has grown in recent years, various light-emitting elements have found practical applications. Among them is a gallium-nitride-based compound semiconductor (In.sub.x Al.sub.y Ga.sub.1-x-y N, 0.ltoreq.X, 0.ltoreq.Y, X+Y.ltoreq.1), which is not only on the current market as a high-intensity blue and green light-emitting diode (LED) but also receiving attention as a prospective material for composing a blue laser diode, a UV sensor, and a solar cell in the future.
FIG. 4A is a plan view of a conventional GaN LED element which is commercially available. FIG. 4B is a cross-sectional view taken along the line B--B thereof. FIG. 4C is a cross-sectional view taken along the line C--C thereof. It is to be noted that the thickness of each semiconductor layer shown in the drawings does not necessarily coincide with the actual thickness thereof. FIG. 5 is a cross-sectional view of a conventional LED lamp which is commercially available. The GaN LED element 40 has a double heterostructure including a GaN buffer layer 31, an n-type GaN layer 32, an InGaN active layer 33, a p-type AlGaN layer 34, and a p-type GaN layer 35 which are stacked sequentially in layers on the top face of a sapphire substrate 30. The top face of the n-type GaN layer 32 has a stepped configuration consisting of an upper-level portion and a lower-level portion. An n-side electrode 36 made of Ti and Au is formed on the top face of the lower-level portion of the n-type GaN layer 32. The aforesaid InGaN active layers 33, the p-type AlGaN layer 34, and the p-type GaN layer 35 are stacked sequentially in layers on the top face of the upper-level portion of the n-type GaN layer 32. A transparent electrode 37 for current diffusion made of Ni and Au is formed on the top face of the p-type GaN layer 35, followed by a p-side electrode 38 formed thereon. Since the GaN LED element 40 is formed by using the insulating sapphire substrate, each of the two electrodes is formed on the top face of the sapphire substrate. The top face of the GaN LED element 40 serves as a light-emitting face, which is coated with a protective film 39 except for the bonding pad portions 36a and 38a of the n-side and p-side electrodes 36 and 38. The GaN LED element 40 is die-bonded to a die pad on the tip of a leadframe 44a via an insulating adhesive 43. The n-side electrode 36 of the GaN LED element 40 is connected to the leadframe 44a via an Au wire 41, while the p-side electrode 38 thereof is connected to a leadframe 44b via an Au wire 42. The respective tip portions of the leadframes 44a and 44b carrying the GaN LED element 40 are molded with a transparent epoxy resin 45 to constitute the LED lamp.
The foregoing conventional light-emitting element has the following problems.
To achieve wire bonding for providing an electrical connection between the GaN LED element 40 and another element or the like as described above, each of the bonding pad portions 36a and 38a should be configured as a circle having a diameter of 100 .mu.m or more or a square having sides of 100 .mu.m or more. Moreover, since the two electrodes 36 and 38 are formed on the light-emitting side, the light-emitting efficiency is degraded. If the bonding pad portions 36a and 38a are provided with a sufficiently large area and the light-emitting face is provided with a sufficiently large area for emitting a sufficient amount of light, the size reduction of the light-emitting element will be limited and the scaling down of the light-emitting element will be difficult.
It is therefore a primary object of the present invention to provide a semiconductor light-emitting element and a manufacturing method therefor, which enable a reduction in the area required by the electrodes to achieve electrical connection of the light-emitting element, the scaling down of the entire light-emitting element, and improvements in the brightness and light-emitting efficiency of the light-emitting element.
Another object of the present invention is to provide a light-emitting device comprising the aforesaid light-emitting element and a manufacturing method therefor.